Scientists investigate chemicals’ ties to obesity

David Epstein |
10/17/2013, 6 a.m.

More than a decade ago, Paula Baille-Hamilton, a visiting fellow at Stirling University in Scotland who studies toxicology and human metabolism, started perusing scientific literature for chemicals that might promote obesity.

She turned up so many papers containing evidence of chemical-induced obesity in animals (often, she says, passed off by study authors as a fluke in their work) that it took her three years to organize evidence for the aptly titled 2002 review paper: “Chemical Toxins: A Hypothesis to Explain the Global Obesity Epidemic.”

“I found evidence of chemicals that affect every aspect of our metabolism,” Baille-Hamilton said. Carbamates, which are used in insecticides and fungicides, can suppress the level of physical activity in mice. Phthalates are used to give flexibility to plastics and are found in a wide array of scented products, from perfume to shampoo. In people, they alter metabolism and have been found in higher concentrations in heavier men and women.

In men, phthalates interfere with the normal action of testosterone, an important hormone for maintaining healthy body composition. Phthalate exposure in males has been associated with a suite of traits symptomatic of low testosterone, from lower sperm count to greater heft. (Interference with testosterone may also explain why baby boys of mothers with higher phthalate levels have shorter anogenital distances, that is, the distance between the rectum and the scrotum).

Baille-Hamilton’s work highlights evidence that weight gain can be influenced by endocrine disruptors, chemicals that mimic and can interfere with the natural hormone system.

A variety of flame retardants have been implicated in endocrine disruption, and one chemical originally developed as a flame retardant — brominated vegetable oil, or BVO — is banned in Europe and Japan but is prevalent in citrusy soft drinks in the U.S. Earlier this year, Gatorade ditched BVO, but it’s still in Mountain Dew and other drinks made by Gatorade’s parent company, PepsiCo. (Many doctors would argue that for weight gain, the sugar in those drinks is the primary concern.)

PepsiCo did not respond to a request for comment, but shortly after the Gatorade decision was made a company spokeswoman said it was because “some consumers have a negative perception of BVO in Gatorade.”

And then there are the newly found zombie chemicals, which share a nasty habit — rising from the dead at night — with their eponymous horror flick villains. The anabolic steroid trenbolone acetate is used as a growth promoter in cattle in the U.S., and its endocrine-disrupting metabolites — which wind up in agricultural run-off water — were thought to degrade quickly upon exposure to sunlight. Until last month, when researchers published results in Science showing that the metabolites reconstitute themselves in the dark.

Says Emily Dhurandhar, an obesity researcher at the University of Alabama-Birmingham: “Obesity really is more complex than couch potatoes and gluttons.”